The Dependence of ITCZ Structure on Model Resolution and Dynamical Core in Aqua-planet Simulations

TitleThe Dependence of ITCZ Structure on Model Resolution and Dynamical Core in Aqua-planet Simulations
Publication TypeJournal Article
Year of Publication2013
JournalJournal of Climate
Abstract / Summary

Aqua-planet simulations using the Community Atmosphere Model version 4 (CAM4) with the Model for Prediction Across Scales - Atmosphere (MPAS-A) and Higher Order Method Modeling Environment (HOMME) dynamical cores and zonally symmetric sea surface temperature (SST) structure are studied to understand the dependence of the inter-tropical convergence zone (ITCZ) structure on resolution and dynamical core. While all resolutions in HOMME and the low-resolution MPAS-A simulations give a single equatorial peak in zonal mean precipitation, the high-resolution MPAS-A simulations give a double ITCZ with precipitation peaking around 2° to 3° on either side of the equator. This study reveals that the structure of ITCZ is dependent on the feedbacks between convection and large-scale circulation. We show that difference in specific humidity between HOMME and MPAS-A can lead to different latitudinal distributions of the convective available potential energy (CAPE) by influencing latent heat release by clouds and the upper tropospheric temperature. With lower specific humidity, the high resolution MPAS-A simulation has CAPE that increases away from the equator that enhances convection away from the equator and through a positive feedback on the circulation, results in a double ITCZ structure. We further show that the dominance of anti-symmetric waves in the model is not enough to cause double ITCZ, and the lateral extent of equatorial waves does not play an important role in determining the width of the ITCZ but rather the latter may influence the former.

DOI10.1175/JCLI-D-13-00269.1
Journal: Journal of Climate
Year of Publication: 2013

Aqua-planet simulations using the Community Atmosphere Model version 4 (CAM4) with the Model for Prediction Across Scales - Atmosphere (MPAS-A) and Higher Order Method Modeling Environment (HOMME) dynamical cores and zonally symmetric sea surface temperature (SST) structure are studied to understand the dependence of the inter-tropical convergence zone (ITCZ) structure on resolution and dynamical core. While all resolutions in HOMME and the low-resolution MPAS-A simulations give a single equatorial peak in zonal mean precipitation, the high-resolution MPAS-A simulations give a double ITCZ with precipitation peaking around 2° to 3° on either side of the equator. This study reveals that the structure of ITCZ is dependent on the feedbacks between convection and large-scale circulation. We show that difference in specific humidity between HOMME and MPAS-A can lead to different latitudinal distributions of the convective available potential energy (CAPE) by influencing latent heat release by clouds and the upper tropospheric temperature. With lower specific humidity, the high resolution MPAS-A simulation has CAPE that increases away from the equator that enhances convection away from the equator and through a positive feedback on the circulation, results in a double ITCZ structure. We further show that the dominance of anti-symmetric waves in the model is not enough to cause double ITCZ, and the lateral extent of equatorial waves does not play an important role in determining the width of the ITCZ but rather the latter may influence the former.

DOI: 10.1175/JCLI-D-13-00269.1
Citation:
2013.  "The Dependence of ITCZ Structure on Model Resolution and Dynamical Core in Aqua-planet Simulations."  Journal of Climate.  https://doi.org/10.1175/JCLI-D-13-00269.1.